1. Field of the Invention
The invention relates to a suspended grid ceiling, and particularly to such ceilings used in clean rooms and other closed environments.
2. The Prior Art
Suspended ceilings used extensively in building construction have a grid of intersecting beams suspended by wires from a structural ceiling. The grid supports panels laid in the grid openings.
The beams are generally formed of a web of flat steel roll formed into an inverted T. The panels are supported on the flanges of the T, with the hanging wires anchored above in the structural ceiling, and connected below to holes in the web of the beam.
The panels, and the upper side of the flanges of the beams, on which the panels rest, have relatively smooth surfaces so that they form a seal tight enough for virtually all ceiling installations.
However, the seal between the beam and the panel must be very tight in clean rooms such as operating rooms, and rooms for sensitive manufacturing operations, as well as rooms where the atmosphere is desirably contained, such as indoor swimming areas.
Various ways to form such very tight seals have been tried. One way was to adhesively apply foam strips to the upper sides of the flanges in the field. This is labor intensive, as each beam must be manually handled to apply the strip. Hold down clips compress the panel on the foam strips.
In another way, flexible tape has been used along the edges of the lower surface of the ceiling panels. This too is labor intensive as the edge of each ceiling panel must be taped manually prior to installation.
In still another way, an aluminum extruded inverted T-beam is used, that has a flat foam gasket applied at the factory. Such beam requires the beam to be specially extruded of aluminum, sometimes with a channel in the flange for the foam gasket, rather than being roll formed of relatively inexpensive steel by continuously passing a flat web of steel through successive rolls. In packing such beams having foam gaskets applied at the factory, the beams are laid in contact with with one another, side-to-side, in a packed container, such as a long cardboard box. The foam on a flange in such packed containers becomes compressed by the adjacent beam, and achieves a permanent set which then creates air leaks when the ceiling is constructed. Such a permanent set also occurs in other ways in beams that use foam gasketing material to seal. For instance, in a magnetic imaging room where heavy panels are inserted, the foam gaskets, with time, become set in a compressed state, and lose resiliency to compensate for any possible movement of the panels.
Other ways to create a seal between a panel and the supporting structure without foam gaskets have been attempted. One way has been to create a U-shaped edge cap around the panels with soft plastic fins extending downward, as in U.S. Pat. Nos. 4,967,530 and 5,033,247. Such an arrangement is labor intensive, since the edge cap must be applied to each panel individually.
In another way, channels in the horizontal flanges are filled with a jelly material. An L-shaped flange on the edge of the panel sinks into the jelly.
The grid beam of the present invention, for a suspended ceiling, has a flexible flap of soft PVC plastic integrally extruded with a hard PVC plastic coating on a rolled steel inverted T-beam. The flexible flap of soft PVC forms a seal with a panel that is supported by the beam. The coating and flap, dually extruded, are continuously formed on the beam at a dual durometer coextrusion station, as the beam emerges from the roll forming operation. As well-known in dual extrusion, the soft PVC that forms the flexible flap is applied to the hard PVC coating while both are in the liquid state, so that the hard and soft PVC are integrally joined.
The dual extrusion compositions and methods used in the present invention are well-known in the prior art. Such methods and compositions are set forth, for instance, in the U.S. Patents cited below and incorporated herewith by reference.
When installed in the ceiling, the grid beam of the invention, before the panel is laid on the flange of the beam, has a resilient flap that extends, and is biased, upward and outward from the upper surface on the flange of the beam at each side of the web. The flap is in effect hinged to the hard plastic coating on the flange, and is integrally connected thereto.
When the panel is laid on a flange the flap yields but continues to be biased upwardly against the panel. Such upward bias of the relatively soft flap against the lower surface of the panel forms a tight seal with the panel, providing, in effect, a relatively airtight closure suitable for a ceiling requiring such tight seals.